The present invention relates to an auxiliary drive of an internal combustion engine for an air compressor. The compressor has a piston that is guided in a cylinder and is driven via a connecting rod by a crankshaft. The crankshaft is connected with a drive gear wheel that is driven by the drive shaft of the internal combustion engine via gear wheels. The air compressor drive gear wheel meshes with a gear wheel on the camshaft.
When compared with V-belt drives, gear wheel driven air compressors of the aforementioned general type have the enormous advantage of a maintenance-free drive. The disadvantage in this case, however, is that the (compressed) air remaining in the cylinder clearance of the air compressor, once the upper dead center position has been reached, expands, with the tangential force that drives the air compressor suddenly becoming negative and the air compressor releasing torque. This leads to a sudden flank change in the tooth mesh accompanied by an unpleasant banging or knocking noise. An additional problem is that the greatest relative noise generation by the air compressor gear wheel drive occurs when the engine is idling after a braking maneuver and the air container is again filled with compressed air (for the compressed air systems, such as the brake system, sliding doors, and the like). Due to the low ignition pressures, the noise of the engine is very low in this case and the flank change of the gear wheel pair is correspondingly clearly noticeable.
A whole series of measures known for eliminating these drawbacks (i.e. reduction of the meshing flank clearance) can be noted as follows:
1. A substitution of the mating of materials of the gear wheel pair from steel to cast iron. PA0 2. The use of a split air compressor clearance compensation gear wheel. PA0 3. A narrowing of the meshing flank clearance by increasing the tooth gauge width. PA0 4. Clearance adjustment by cam adjustment.
All of these measures are either expensive to manufacture or are space-consuming and structurally complicated and necessitate additional expenditure at the engine assembly line respectively with an air compressor exchange in the factory. In addition to this, the possibility of faults and inaccuracies as a result of individual adjustment practices is high. However, the greatest disadvantage associated with clearances which are too small is the increased axial pressure that is exerted over the entire circumference of the air compressor bearing and the air compressor crankshaft as well as of the camshaft and crankshaft bearings. With drive shafts having roller bearings, radial loads represent seriously impaired operating conditions. With drive shafts having friction bearings, a high bearing temperature and premature bearing failure result from the constant axial pressure. This finally results in a reduced service life of the entire air compressor arrangement.
It is an object of the present invention to reduce the noise generation of the tooth flanks, in particular in the region of the upper dead center position of the air compressor piston, while also avoiding increased rotational bending strain on the air compressor crankshaft and the camshaft.